Angband

Like nethack, moria,
and rogue, one of the large freely distributed
Dungeons-and-Dragons-like simulation games, available for a wide
range of machines and operating systems. The name is from Tolkien's
Pits of Angband (compare elder days, elvish). Has been
described as "Moria on steroids"; but, unlike Moria, many aspects
of the game are customizable. This leads many hackers and would-be
hackers into fooling with these instead of doing productive work.
There are many Angband variants, of which the most notorious is
probably the rather whimsical Zangband. In this game, when a key
that does not correspond to a command is pressed, the game will
display "Type ? for help" 50% of the time. The other 50% of the
time, random error messages including "An error has occurred
because an error of type 42 has occurred" and "Windows 95
uninstalled successfully" will be displayed. Zangband also allows
the player to kill Santa Claus (who has some really good stuff, but
also has a lot of friends), "Bull Gates", and Barney the Dinosaur
(but be watchful; Barney has a nasty case of halitosis). There is
an official angband home page at
http://www.phial.com/angband and a zangband one at
http://thangorodrim.angband.org. See also Random Number God.

Now, I know, some of you really hate ASCII art. Well, you can leave now, or read on. This is not ASCII art. This is the actual playing screen of the game. Every character on screen has a meaning, it's not just there to build up a pretty picture:

The point of the ASCII graphics is that Angband is portable to a huge number of platforms, and best of all, it is blindingly fast. No time is wasted drawing animated little cartoon warriors swinging little cartoon swords at you. You run into something, hit it, it hits you, somebody dies. You get in far, far more play time, actually doing something, than in any other computer game. And it's not a twitch game; it is strictly turn-based, so if you have to go take the teakettle off the burner, you haven't died by the time you get back.

Angband is also a testimony to the right way to do open source. It is quite simply one of the finest, most stable, best documented, most configurable pieces of software in existence -- of any kind. I strongly urge you to try it today.